A motion guide apparatus where a carriage is assembled to a track member via a rolling element in such a manner as to be relatively movable is known as a motion guide apparatus that guides linear motion of a movable body, such as a table, of a machine tool. The rolling element is interposed between the track member and the carriage; accordingly, it is possible to eliminate a gap between the track member and the carriage and support the movable body with high rigidity. Moreover, the rolling element performs rolling motion between the track member and the carriage; accordingly, the movable body performs smooth linear motion.
A magnetic or optical scale that is affixed to the track member is known as the position detection apparatus used for the motion guide apparatus. A magnetic or optical sensor that reads the scale is attached to the carriage (refer to, for example, Patent Literature 1). The track member is provided with a groove along a longitudinal direction. The scale is fitted in the groove.